33] THE HEAD-CAPSVLE OF COLEOPTERA— STICKS EY 33 



gestive of the sternellum, and the smaller one would then represent their 

 "sternum." It is generally stated that the gula is derived from the chitini- 

 zation of the neck membrane or cervix. In the discussion preceding, 

 dealing with the metatentorinae and the postgenae, I have attempted to 

 show the impossibihty of such a derivation. In many orders of insects 

 structures on the caudal aspect of the head have been designated as the 

 gula- My interpretation would prevent the recognition of the presence 

 of the gula in any insects other than the Coleoptera, Neuroptera, and 

 Trichoptera. 



In some Coleoptera there is no gula (Figs. 168, 177, and possibly 286), 

 whereas in others there is a complete gula (Figs. 150, 157, 172, 185, 267, 

 and 296). Between these extreme types there are found in the Coleop- 

 tera all gradations of a gula in process of formation (Figs. 156, 187, 210, 

 245, and 257). Such a range of variation in a structure simply emphasizes 

 the importance of a comparative study of a large series of forms. The 

 question as to which is the more generalized condition, the presence of a 

 complete gula or the absence of one, has been previously discussed, with 

 the verdict in favor of the latter condition. It would then be impossible, 

 other reasons not being considered, for the gula to be the sternum of the 

 cervical segment. The gula is the sclerite formed by the migration of the 

 metatentorinae from the occipital foramen towards the submentum, and 

 must be derived from the postgenae. In this migration of the metaten- 

 torinae sutures are produced which are known as the gular sutures. The 

 area between the gular sutures is the gula. It is evident, then, that the 

 presence and extent of the gula depend upon the position of the metaten- 

 torinae and the sutures which they produce. The gula is complete in all 

 the Adephaga except Peltodytes (Fig. 156), in the Silphidae, the Staphy- 

 linidae, the Sphaeriidae, the first four families of the Canthroidea, and the 

 Scarabaeidae except Pseudolucanus (Fig. 266). Isolated examples in 

 other families of a complete gula are Scaphidium (Fig. 179), Helichus 

 (Fig. 214), Cyphon (Fig. 220), Byrrhus (Fig. 223), and Leptinotarsa 

 (Fig. 278). The gular sutures nearly meet in Gastrolobium (Fig. 171) 

 and Creophilus (Fig. 172), and are entirely confluent in Necrophorus 

 (Fig. 166), Scaphidium (Fig. 179), Hister (Fig. 181), Phengodes (Fig. 184), 

 Chauliognathus (Fig. 185), and in all the Rhynchophora except Eurymycter 

 (Fig. 286) and Rhinomacer (Fig. 287) in which genera the gular sutures 

 are very widely separated. In Rhinomacer the gular sutures extend nearly 

 half the distance to the submentum. The gula in cases of confluency of 

 the middle portion of the gular sutures on the meson is simply invaginated. 

 The gula is complete but extremely short in Calopteron (Fig. 182) and 

 Photinus (Fig. 183). The cephalic ends of the gular sutures meet on the 

 meson near the occipital foramen in Philothermus (Fig. 240) and Anoplitis 

 (Fig. 280). The gula is partially membranous in Nosodendron (Fig. 224), 



